The present invention relates to a capacitor in a semiconductor device; and, more particularly, to a method for fabricating the capacitor constituted with double hafnium oxide layers formed through a plasma enhanced chemical vapor deposition (PECVD) process and a low pressure chemical vapor deposition (LPCVD) process.
As a semiconductor memory device is highly integrated, size of a unit cell thereof is decreased, and size of a capacitor constituting the unit cell is also decreased. Along with the reduced size, the capacitor for storing a data should secure enough amount of electrical charge to guarantee a stable operation of the semiconductor memory device.
The enough amount of electrical charge can be obtained by increasing an active surface area of the capacitor. As a most preferable method, the increased active surface area of the capacitor can be obtained by increasing height of the capacitor. However, the method mentioned above makes it difficult for a etch process to be carried out. Accordingly, the method is hardly ever applied to a capacitor fabrication.
A Ta2O5 layer is usually used for forming the capacitor. However, a thermal stability of the Ta2O5 layer is poor, and a dielectric constant of the Ta2O5 is low. Therefore, enough capacitance to operate the semiconductor memory device can not be obtained. To overcome the problems mentioned above, the Ta2O5 layer is substituted with a HfO2 layer.
The dielectric constant of HfO2 is higher than that of Ta2O5. Also, the thermal stability and a current leakage property of the HfO2 are superior to those of Ta2O5, and therefore, it is possible to secure enough capacitance to operate the semiconductor memory device.
According to a prior art, an atomic layer deposition (ALD) method is conventionally used to form the capacitor constituted with the HfO2 layer because it is possible to get a good step coverage and form the HfO2 layer containing few impurities. Also, a low pressure chemical vapor deposition (LPCVD) method can be used to form the capacitor constituted with the HfO2 layer. At this time, a process throughput time can be decreased by the LPCVD method, and therefore, process productivity can be increased.
However, in case of the ALD method, it takes much time to perform the ALD process and thereby, increasing the process throughput time and decreasing the productivity.
In case of the LPCVD method, it is impossible to get a good quality of HfO2 layer. Therefore, processes for removing the impurities from the HfO2 layer are required. More specifically, to remove the impurities, a first heat treatment is carried out at a low temperature ranging from about 300xc2x0 C. to about 500xc2x0 C. through a O2 or N2O plasma treatment process. A second heat treatment using a conventional furnace is then carried out at a high temperature ranging from about 500xc2x0 C. to about 650xc2x0 C. in oxygen ambient. However, the heat treatment processes mentioned above are complicated, and the impurities inside the HfO2 layer can not be removed effectively.
It is, therefore, an object of the present invention to provide a method for fabricating the capacitor constituted with double hafnium oxide layers formed through a plasma enhanced chemical vapor deposition (PECVD) process and a low pressure chemical vapor deposition (LPCVD) process.
In accordance with an aspect of the present invention, there is provided the method for fabricating the capacitor, including: forming a lower electrode over a semiconductor substrate; performing a heat treatment with the lower electrode; forming a first HfO2 layer over the first HfO2 layer by using a plasma enhanced chemical vapor deposition (PECVD) method; forming a second HfO2 layer over the first HfO2 layer by using a low pressure chemical vapor deposition (LPCVD) method; performing a plasma treatment process at a high temperature; and forming an upper electrode over the second HfO2 layer.